A field bus is a bus through which communications between field devices, in service at a factory, and so forth, are carried out.
The field devices in number ranging from several tens to several hundreds are connected to the field bus, and mutual communications between the field devices are carried out via the field bus. By use of the field bus, wiring cost can be reduced, and change/expansion of a system can be flexibly coped with.
The field bus is comprised of two hierarchies, that is, H1 bus, and HSE {High Speed Ethernet (the registered trade name)} bus. While H1 bus has a communication speed at 31.25 kbps, HSE bus is capable of high speed communication, because it is based on Ethernet.
Since HSE bus is based on Ethernet (the registered trade name), communications are executed by use of IP (Internet Protocol). For IP, there exist two protocols, including IPv4 having 32 bits address space, and IPv6 having 128 bits address space. As IP is in the process of transition from IPv4 to IPv6 at present, those two protocols coexist for IP. For execution of communications between a communication device according to IPv4 (an IPv4-capable device) and a communication device according to IPv6 (an IPv6-capable device), IP addresses must be mutually translated.
FIG. 9 shows a system configuration comprising both the IPv4-capable device, and the IPv6-capable device. In FIG. 9, reference numerals 10, 12 denote the IPv6-capable device, and the IPv4-capable device, respectively, while reference numerals 11, 13 denote networks with the devices 10, 12, connected thereto, respectively. The IPv6-capable device is connected to the network 11, and the IPv4-capable device is connected to the network 13.
Reference numeral 14 denotes a gateway unit connecting the network 11 to the network 13. When the IPv6-capable device 10 transmits a packet to the IPv4-capable device 12, an IP address of the transmitted packet is translated into an IPv4 address by the gateway unit 14. Similarly, when the IPv4-capable device 12 transmits a packet to the IPv6-capable device 10, an IP address of the packet is translated from the IPv4 address into an IPv6 address by the gateway unit 14. By so doing, a packet can be mutually translated between the IPv6-capable device 10, and the IPv4-capable device 12.
FIG. 10 is a configuration diagram showing a configuration of the gateway unit 14. In the figure, parts of the gateway unit 14, unrelated to IP address translation, are omitted in description thereof. In FIG. 10, a packet receiving section 14a delivers a received packet to an IP translating section 14b. The IP translating section 14b translates an IP address in the header of the packet as received from IPv4 to IPv6, or in a direction reverse thereto.
At this point in time, the IP translating section 14b makes reference to translation rules stored in a translation rules storage section 14d, thereby translating the IP address. The packet subjected to address translation is inputted to a packet transmitting section 14c before transmission. The translation rules to be stored in the translation rule storage section 14d are normally configured by an operator in advance to be set in the gateway unit 14 prior to operation.    [Patent Document 1] JP 2002-132309 A    [Patent Document 2] JP 2005-531229 A